Previously, outboard marine engines have often utilized various means for accomplishing easier starting. For example, such engines may engage a "warm-up" lever which manually advances the ignition timing and partially opens the carburetor throttle plates. The function of such arrangement is to increase the idle speed and the air/fuel ratio of the engine when it is started. These conditions allow the engine to start easier and run more smoothly until it has warmed up to its standard operating temperature.
While many other engine ignition systems have utilized various means to selectively advance the ignition timing characteristic during operation, none of these systems has been adapted to selectively change the engine timing characteristic as a function of the temperature of the engine during its warm-up phase, as well as during a predetermined time period regardless of the temperature of the engine, and as a function of the operating speed of the engine, particularly when operated at a relatively high speed.
A multi-variable ignition system for outboard marine engines or the like, which selectively adapts ignition scheduling on this basis is illustrated in the referenced parent application, U.S. patent application Ser. No. 131,457, entitled, "Electronically Assisted Engine Starting Means" by Gregry M. Remmers, which was filed on Dec. 11, 1987, and which is assigned to the assignee of the present invention. The disclosure of Remmers is hereby expressly incorporated by reference herein.
The system of Remmers provides an improved ignition system which utilizes a signal proportional to the speed of the engine and couples such speed signal with other signals representing additional engine operating conditions to selectively modify the ignition timing characteristic of the engine to accomplish the functional operational characteristics of: (1) providing protection against engine damage that may be caused by a runaway speed condition; (2) providing a desirable ignition advance during the warm-up period of the engine; (3) providing a desirable ignition advance during the initial engine start up period, irrespective of the temperature of the engine (i.e., even when the engine is warm as a result of having been previously operated); and (4) providing protection against damage that may be caused by advancing the timing characteristic while operating the engine above a predetermined operating speed.
The system as taught in Remmers, while advantageous in the adjustment of ignition timing in dependence on a variety of engine operating conditions, does not exhibit the most advantageous time base generator or means for distributing the ignition pulses. The time base for that system is derived from two sets of coils, each of which is associated with a particular cylinder and crankshaft position. One set of coils is physically advanced with respect to the other set to generate two sets of timing pulses; one a normal pulse train and the other an advanced pulse train. Magnets on the flywheel or crankshaft fire each coil in succession to generate the two pulse trains, and engine operating conditions are combined to determine which set of pulses is used to ignite the engine.
Such time base generator is simple and easy to use in small engines, but with higher displacement engines two ignition coils per cylinder becomes somewhat more difficult to package. Further, for multiple cylinder engines, those with four or more cylinders, it is desireable to produce a schedule of ignition advance based on a plurality of engine operating conditions, most typically, one that varies with throttle position. This scheduling is difficult to accomplish with a dual ignition coil time base generator.
Moreover, in Remmers, when inhibiting ignition pulses relative to overspeed and overheated engine conditions, an overspeed threshold is switched immediately from one level to another level when an overheated condition occurs. For small displacement outboard marine engines, an overheated engine condition many times results when the engine is under considerable load, usually pushing a boat along at a high rate of speed. Inhibiting the ignition pulses without any transition between the threshold levels under these conditions can cause a rapid and disconcerting deceleration. Therefore, it would be advantageous to provide a slower transition between the threshold levels so that, if an overheated condition occurs during such a high load condition, a slower and more acceptable deceleration will occur.